Towards frameless maskless SRS through real-time 6DoF robotic motion compensation

Abstract

Purpose Stereotactic radiosurgery (SRS) uses precise dose placement to treat conditions of the CNS. Frame-based SRS uses a metal head ring fixed to the patient’s skull to provide high treatment accuracy, but patient comfort and clinical workflow may suffer. Frameless SRS, while potentially more convenient, may increase uncertainty of treatment accuracy and be physiologically confining to some patients. By incorporating highly precise robotics and advanced software algorithms into frameless treatments, we present a novel frameless and maskless SRS system where a robot provides real-time 6DOF head motion stabilization allowing positional accuracies to match or exceed those of traditional frame-based SRS. Methods A 6DOF parallel kinematics robot was developed and integrated with a real-time infrared camera in a closed loop configuration. A novel compensation algorithm was developed based on an iterative closest-path correction approach. The robotic SRS system was tested on six volunteers, whose motion was monitored and compensated for in real-time over 15-minute simulated treatments. The system’s effectiveness in maintaining the target’s 6DOF position within preset thresholds was determined by comparing volunteer head motion with and without compensation. Results Comparing corrected and uncorrected motion, the 6DOF robotic system showed an overall improvement factor of 21 in terms of maintaining target position within 0.5 mm and 0.5 degree thresholds. Although the system’s effectiveness varied among the volunteers examined, for all volunteers tested the target position remained within the preset tolerances 99.0% of the time when robotic stabilization was used, compared to 4.7% without robotic stabilization. Conclusion The pre-clinical robotic SRS compensation system was found to be effective at responding to sub-millimeter and sub-degree cranial motions for all volunteers examined. The system’s success with volunteers has demonstrated its capability for implementation with frameless and maskless SRS treatments, potentially able to achieve the same or better treatment accuracies compared to traditional frame-based approaches.

Frame-Based and Mask-Based Stereotactic Radiosurgery: The Patient Experience, Compared

“…In terms of patient perspectives, current literature cites FB procedures as invasive, anxiety-inducing, and potentially painful [4,[11][12][13]. In 2002, St George et al [14] contacted 47 patients 2-3 weeks post SRS and found that a third of them were still experiencing pain/numbness at the pin site.…”

“…We prefer to avoid the term "frameless" as it is more accurate to describe a procedure by what it is rather than what it is not. In a FB procedure, a rigid frame is fixed to the patient's skull to suppress voluntary and involuntary movements under local anesthetic delivery and intravenous analgesia [4]. MB SRS, comparatively, utilizes a noninvasive thermoplastic custom-molded mask to the patient's face in order to immobilize the patient [5].…”

“…One advantage of FB SRS, certainly from a neurosurgical perspective, is that the workflow has little variance and has been the mainstay of SRS for over 50 years [6,10]. However, frame application is somewhat invasive and can cause patient pain and anxiety [4]. Despite the use of oral or intravenous sedation and local anesthetic, patients can still experience pain from the screws for the frame, in addition to scarring and potential infection [11][12][13][14].…”

“…In fact, clinicians are attributing the possibility of fractionation in MB procedures as a factor that increases the number of patients eligible for SRS treatment [11]. The mask can, however, still be uncomfortable (if not "painful" per se), restrictive, and is not ideal for patients who are restless, anxious, and/or claustrophobic [4,6,18]. Despite these commonly cited advantages and disadvantages, there are few studies that directly and quantitatively investigate the patient experience of SRS.…”

A conceptual study on real-time adaptive radiation therapy optimization through ultra-fast beamlet control

“…A wide variety of methods have been proposed for directly addressing such intrafractional motion. Among the most advanced, is the use of real-time patient motion compensation, where prior works include the use of a robotic arm to move a compact LINAC in sync with a tumor (Adler Jr, Chang, Murphy, Doty, Geis & Hancock 1997) Liu, Belcher, Grelewicz & Wiersma 2015, Belcher, Liu, Grelewicz, Kamil & Wiersma 2017. However, these methods typically employ a static treatment plan, and do not dynamically adapt this plan to real-time changes in patient anatomy.…”